A dual-mode transducer in the traveling wave rotary ultrasonic motor to extend the high-efficiency speed range

This study proposes a dual-mode transducer design for the traveling wave rotary ultrasonic motor (TRUM) to address the inherent limitation of narrow high-efficiency speed ranges in conventional single-mode counterparts, which critically hinder their applicability in aerospace systems requiring sustained low-speed operation and transient high-speed adjustments. By synergistically integrating low-order (B03) and high-order (B09) vibration modes, the motor achieves enhanced electromechanical efficiency across an extended operational speed spectrum. A Kirchhoff plate-based dynamic model establishes the quantitative relationship between modal characteristics and performance metrics, revealing that low-order modes amplify torque capacity through larger amplitudes, while high-order modes prioritize speed via elevated tangential velocities. Perturbation theory predicts asymmetric modal splitting susceptibility, demonstrating that low-order modes exhibit higher splitting propensity than high-order modes under equivalent manufacturing imperfections-validated experimentally through laser Doppler vibration scanning. Finite element-driven structural optimization enhances B03 and B09 mode amplitudes by 78 % (1400-2500 nm) and 63 % (800-1300 nm), respectively. Prototype characterization confirms the dual-mode TRUM achieves peak efficiencies of 17.7 % (B03 mode) and 16.5 % (B09 mode), with a 47 % broader high-efficiency speed range compared to single-mode configurations. A perturbation-theoretic correction method effectively mitigates B03 mode splitting, improving stall torque by 80 % and efficiency by 30.9 % without destabilizing B09 modal dynamic. The proposed methodology advances precision motor design through mode-switching strategies, modal splitting control, and multi-physics optimization, offering a paradigm for next-generation high-efficiency ultrasonic actuators.